In high volume institutional food preparation and service installations, chemical sanitizing compositions are often used in manual and automated ware washing processes to destroy bacteria during rinsing operations to meet minimum sanitation standards. In many installations sanitation standards are met through the use of very high temperature rinse water (180.degree.-195.degree. F.). Where such temperatures are not achievable, a chemical sanitizing agent is often added to one or more aqueous materials that contact kitchenware or tableware to produce a bacteria killing effect at the low temperature conditions of approximately 120-140.degree. F. The use of the terms "high temperature" and "low temperature" herein relate approximately to the above temperature ranges.
Low temperature methods and equipment are illustrated in the following, Fox et al., U.S. Pat. Nos. 2,592,884, 2,592,885, and 2,592,886, 3,044,092 and 3,146,718, as well as Fox, U.S. Pat. No. 3,370,597. In large part, these machines follow a cleaning regimen wherein the soiled kitchenware or tableware can be prescraped either manually or with an automatic machine scraping stage involving a water spray to remove large bulk soil. The ware can then be directed to a zone wherein the ware is contacted with an aqueous alkaline cleaning composition that acts to remove soil by attacking protein, fat or carbohydrate soils chemically. The cleaned ware can be first rinsed and then be directed to a sanitizing stage wherein the ware is contacted with sanitizer material. Alternatively, the ware may be directed to a combined rinsing-sanitizing stage where the ware is contacted with a combination of rinse agent and sanitizer. Lastly, the ware can be directed to a stage where the articles are dried either actively by heating or passively by ambient evaporation.
The need for sanitization has lead to the consideration of various agents. One of the most common sanitizers for ware washing is aqueous sodium hypochlorite (NaOCl). However, while sodium hypochlorite is effective, low cost and generally available, sodium hypochlorite has several disadvantages. First, hypochlorite can react with hardness ions in service water including calcium, magnesium, iron, manganese, etc. Such chemical interaction can cause liming and mineral deposits on machine parts. Such deposits can tend to form in and on the water passages of a ware washing machine which can substantially change the flow rates of various aqueous materials through the machine. Any such change can seriously reduce the effectiveness of machine operation. Chlorine, as a constituent of sodium hypochlorite, may also present compatibility problems when used with other chemicals which have desirable sheeting and rinse aid characteristics, such as nonionic surfactants. Further, the interaction between sodium hypochlorite and various minerals in service water can result in the spotting and filming of ware products.
Sodium hypochlorite use tends to substantially increase the total dissolved solids present in aqueous sanitizing compositions. High concentrations of solids can tend to increase the tendency of agents to leave unwanted spotting and streaking upon drying. In fact, while chlorine has a noted sanitizing effect, the increased solids resulting from this constituent can film, spot and otherwise leave a residue on ware products subjected to the rinse. Chlorine may also react and degrade or corrode tableware comprising metals as well as metals found in the environment of use.
Sodium hypochlorite is also a strong oxidizing chemical and can substantially corrode a variety of materials used in machine manufacture and in tableware and kitchenware commonly used in today's institutional environment. Chlorine may also react and degrade or corrode tableware comprising silver or a silver plate finish. The degradation product is the reaction product of silver and other elemental ions in which the silver metal comes into contact. Silver rapidly compounds to form, for example, silver oxides and silver halogens, in particular silver chloride when exposed to chlorine from, for example, sodium hypochlorite.
In the meantime, various rinse aid compositions have been developed for use in both low temperature and high temperature wash systems. For example, Fraula et al., U.S. Pat. No. 4,147,559 and Reissue U.S. Pat. No. 30,537 teach an apparatus and a method for rinsing and chemically sanitizing foodware items. The disclosure is primarily directed to machine related components for ensuring adequate cleaning and sanitizing.
Further, a number of rinse aid compositions, based largely on nonionic surfactants without sanitizers are also known. Altenschopfer, U.S. Pat. No. 3,592,774, teaches saccharide-based nonionic rinsing agents. Rue et al., U.S. Pat. No. 3,625,901, teach surfactants used as rinse aids having low foaming properties. Dawson et al., U.S. Pat. No. 3,941,713, teach machine ware washing rinse agents having an anti-resoiling or non-stick additive for treating aluminum or other such metal kitchenware. Rodriguez et al., U.S. Pat. No. 4,005,024, teach a rinse aid composition containing organosilane and monofunctional organic acids that act as rinse agents. Herold et al., U.S. Pat. No. 4,187,121, teach a rinse agent concentrate based on saccharide glycol ether technology.
Further, Morganson et al., U.S. Pat. No. 4,624,713, teach a solidified rinse agent composition containing a nonionic rinsing agent, urea, water and other components. Surveys of nonionic surfactants and rinse additives containing nonionic surfactants are found in Schick, "Nonionic Surfactants", published by Marcel Dekker, and John L. Wilson, Soap and Chemical Specialties, February 1958, pp. 48-52 and 170-171.
However, none of these rinse aids have been able to combine effective sheeting and rinsing action with sanitizing efficacy. Accordingly, a strong need exists in the art to provide a rinsing sanitizing agent that can promote sheeting and prevent spotting, provide substantial sanitizing action, work safely within the environment, and result in operations without any substantial deposit formation on ware, dish machines or corrosion of machine components or kitchenware, tableware, and particularly ware products comprising silver.
While peroxyacid containing concentrates have been described in U.S. Pat. Nos. 4,051,058 and 4,051,059, these patents do not focus on the desired properties above described. The present invention provides for the use of an improved concentrate containing higher levels of peroxyacetic and acetic acid and a lower level of hydrogen peroxide.